1. Field of the Invention
The present invention relates to a submerged motor pump which comprises a motor and a pump combined with each other as a unitary assembly and has a thrust balancing mechanism, and more particularly to a submerged motor pump having an auxiliary bearing assembly for supporting a rotatable main shaft when the submerged motor pump operates in a transient condition.
2. Description of the Related Art
Hydrostatic bearings used in a submerged motor pump which produce a load capacity under the pressure of a pressurized fluid pumped by the pump support a rotatable main shaft of the pump in a noncontact state by utilizing the static pressure of a fluid in a small chamber which is normally referred to as a pocket.
A submerged motor pump uses a liquid pumped thereby as a pressurized fluid for hydrostatic bearings. When a submerged motor pump is not operating, or is in a transient condition, i.e., it is in a starting operation or a stopping operation, the pressure of the fluid discharged from the pump is not sufficiently high, and thus the hydrostatic bearings fail to achieve their sufficient performance. Therefore, the submerged motor pump normally uses ball bearings as auxiliary bearings, in addition to the hydrostatic bearings, for supporting the main shaft of the pump. The ball bearings serve to support the main shaft only when the pump is not in an operating condition or is in a transient condition. While the pump is operating in a normal condition where the pressure of the fluid discharged from the pump is sufficiently high, axial loads (i.e., axial thrusts) are balanced by a thrust balancing mechanism, and the main shaft is supported by the hydrostatic bearings. At this time, since the ball bearings do not support the main shaft, the ball bearings are arranged such that they are free from any loads from the main shaft.
The ball bearing has a cylindrical bearing surface, and a small gap is formed between the cylindrical bearing surface of the ball bearing and the outer circumferential surface of the main shaft. This gap is smaller than the gap between the hydrostatic bearing and the main shaft in order to prevent the hydrostatic bearing from contacting the main shaft when the pump is operating in the transient condition. However, the gap between the ball bearing and the main shaft cannot be made zero, but is set to an appropriate value. When the pump is operating in the transient condition, the ball bearing cannot prevent the main shaft from wobbling in the gap, i.e., cannot support the main shaft stably enough to avoid excessive vibrations and various phenomena responsible for accidents.